This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Obstructive and restrictive lung diseases such as emphysema, asthma, and cystic fibrosis adversely affect gas flow in the lungs, and therefore compromise regional lung ventilation. Noninvasive assessment of regional lung function is therefore of critical importance in quantifying the severity of the disease, evaluating response to therapy, and predicting the clinical outcome. Pulmonary function tests (such as spirometry and diffusing capacity) provide an inexpensive, yet insensitive and only a global measure of lung function, which can be insensitive to regional lung abnormalities. Other common clinical lung imaging techniques (such as radionuclide ventilation-perfusion scintigraphy and radioactive aerosols) provide qualitative information about regional ventilation and suffer from poor spatial resolution and exposure to radioactive materials. Quantitative techniques based on delivery/ clearance rates xenon-contrast CT images have also been developed. The emergence of hyperpolarized (HP) 3He MRI however has provided a unique set of capabilities in noninvasive visualization of ventilated airspaces. Earlier techniques developed to measure lung ventilation using this technology were limited to use in rodents, since they utilize many HP 3He breaths and consequently require a relatively long acquisition time and an infeasible amount of 3He available in one imaging session. The fractional ventilation imaging technique developed in this project can be performed much faster, requires substantially fewer 3He breaths, and is shown to be in good agreement with older methods as demonstrated in rodents. These features make this technique a suitable approach in ventilation imaging in larger species as well as in human subjects.